The present invention relates to brake discs and in particular aircraft brake discs of carbon-carbon composite material comprising a substrate of carbon or graphite fibres embedded in a carbon matrix, and methods of manufacture thereof.
It is known that carbon-carbon composite materials are generally produced by preparing a substrate of carbon or graphite fibres, which is then subjected to a carbon densification treatment.
It is also known that the substrate may be made either using long fibres which are organized in different ways (two-dimensional or three-dimensional weaving processes, a needling operation, etc), or with relatively short fibres which are oriented in a partially or totally random fashion.
The present invention is only concerned with composite materials which are formed from short fibres, that is to say for example fibres which are from 0.01 to 6 cm in length.
In order to produce a component in the form of a brake disc, it is known that the short fibres may be arranged ether in a random manner with respect to the volume or the friction surfaces of the disc, or in an axisymmetrical manner with respect to the axis of the disc.
The present invention is not concerned with brake discs comprising axisymmetrical fibres.
Moreover, it is known that there are three important qualities regarding a brake disc;
good resistance to the braking torque,
good resistance to friction, and
low coefficient of expansion in regard to thickness.
The known brake discs comprising non-needled, non-axisymmetrical short fibres essentially have the first quality (in that the fibres are preferentially disposed in planes which are almost parallel to the friction planes and are randomly oriented in such planes. The length of the fibres used in that case is generally greater than the thickness of the disc).